1. Field of the Invention
This invention relates to light refractive coated paper board, milk carton board, papers and the like and more specifically, it relates to light refractive coated paper board which mask the stains produced by grease penetration into the substrate stock. The invention also includes the method of making such light refractive coated paper board products.
2. Discussion of Prior Art
Large sums of money are spent on designing packaging materials to enhance the attraction to the consumer for the product contained therein. The design encompasses not only the size and shape of the package but more importantly, the color and graphics printed on the package. Obviously, if the nature of the packaged product is such that it produces materials such as oils and greases which can penetrate the packaged materials and stain the exposed surface of the package, the aesthetic appearance of the package is greatly reduced as is, most probably, its attraction to the consumer.
Previous efforts towards eliminating the problem of stains produced by oil and grease penetration into the packaging stock have been directed at preventing the grease from penetrating into the stock. Foil laminated packaging stock could be used but is relatively expensive. Other methods of preventing grease penetration into the stock which have heretofore been employed are polyolefin coatings, fluorocarbon coatings, saturation with paraffin or microcrystalline waxes, coating one or both sides of the stock with polymer fortified waxes, and the like; however, these have generally proven to be unsuccessful.
U.S. Pat. No. 3,463,659 describes the use of a barrier coating over a paper substrate. This base coating consists of 52-88% inorganic pigment such as clay, calcium carbonate or titanium dioxide, 2-20% thermoplastic pigment having a glass transition temperature greater than 150.degree. F., 5-25% of synthetic emulsion polymer adhesive and 5-25% of a water or alkali soluble adhesive such as starch, casein or protein. The function of this base coat is to fill, smooth and solvent-proof the surface of the paper substrate. This base coat also can be applied to the underside of the paper substrate to prevent curling. If the paper substrate is not filled and smoothed by one application of the base coat, more of this relatively expensive coating can be employed. The base coat layer is further smoothed and densified by super calendering. The base coat is then covered by a lacquer over coat followed by a vacuum deposited metal film. The lacquer over coat must provide the mechanism for building the physical characteristics that are desired in the final sheet e.g., oil resistance. The resulting metallized paper can be further primed for printing with a lacquer top coat and is reported to possess excellent oil resistance i.e., exposure of the backside of the metallized paper would provide, in addition to a moisture barrier, a barrier to grease and oils.
In many instances, it is either undesirable to employ a metallized substrate as a packaging material, particularly where exterior coloration and/or printing is desired on the surface of the package, or it is impractical or too expensive to employ a barrier to oil and/or grease absorption. In such instances, it would be desirable to provide an easily printable packaging material which could mask the appearance of unsightly oleaginous stains from the eyes of a prospective purchaser.
Accordingly, it is an object of the present invention to produce a light refractive coated paper board which conceals grease or oil stains absorbed by the inner surface of the substrate which would otherwise normally mar the appearance of the outer surface of the finished structure.
It is another object of the present invention to provide a coated paper board which conceals stains which would distract from the aesthetic appearance of the printing, color and/or shape of the individual package.
Yet another object of the invention is to duplicate almost exactly the appearance of a colored foil laminated paper board without the use of foil, characterized by light refractive properties imparting enhanced effectiveness for masking grease.
It is still another object of the present invention to provide a method for making such light refractive coated paper board in an economically feasible and simple manner.